Molten magnesium supply system

Details Molten magnesium supply system Molten magnesium supply system

1999-10-25

2002-01-01

Andrews, Melvyn (Department: 1722)

Metallurgical apparatus

With control means responsive to sensed condition

With means responsive to condition of treated material

C164S155200, C222S603000, C266S237000

Reexamination Certificate

active

06334975

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a molten magnesium supply system as well as to a molten magnesium supply method, and in particular, to a molten magnesium supply system that is constituted with a molten magnesium supplying apparatus for a die casting machine of a cold chamber type for casting molten magnesium (with molten magnesium alloy inclusive), or includes a melting and holding furnace for melting a magnesium ingot and holding molten magnesium to be supplied to an injection sleeve of a die casting machine, or an ingot charging apparatus for charging a preheated magnesium ingot into a melting and holding furnace, as well as to a molten magnesium supply method that includes charging a preheated magnesium ingot into a melting and holding furnace, melting the ingot in the furnace, holding molten magnesium in the furnace, and supplying molten magnesium to an injection sleeve of a die casting machine.
2. Description of the Related Art
Cold-chamber die casting needs fresh and homogeneous molten metal to be continuously and instantaneously injected under high pressure into recesses of a cavity in a mold. For such injection, the die casting machine has an injection sleeve, and is provided with a supply system for supplying molten metal to the injection sleeve. The supply system is adapted for a conforming supply of molten metal meeting various requirements, such as for molten metal amount or quantity to be accurate and nature or quality to be controlled and stable in consideration of molding conditions.
In the case of magnesium, the molten metal has a significant tendency to be oxidized, and needs an air-free supply to the injection sleeve via pipe, duct, etc. For such supply, one may employ a molten metal transfer mechanism or molten metal transferring means for forcing molten metal to advance in a molten metal transfer pipe. The molten metal transfer mechanism or molten metal transferring means may be of a volume displacement type such as by use of a screw pump, or of a fluid streaming type such as by use of an electromagnetic pump in which a fluid flow rate is controlled with an electric current in an exciting coil around a fluid circuit.
A typical molten magnesium supply system is constituted with a molten magnesium supplying apparatus including a melting and holding furnace and sometimes provided with a preheater for preheating a magnesium ingot.
FIG. 1
illustrates a conventional molten metal supply system. The system comprises a furnace body Fb of a “magnesium melting and/or molten magnesium holding furnace (hereinafter sometimes called “molten metal furnace”)
55
and a molten metal transfer pipe
52
extending therefrom. The transfer pipe
52
is constituted at a suction inlet end thereof with an outlet port Fp of the furnace
55
communicating with an inside of the furnace body Fb, and along the remaining length thereof with a heated transfer tube Tb flange-joined to the port Fp. An electromagnetic pump
50
is installed on the inlet end of the pipe
52
. The transfer pipe
52
is formed at a delivery end thereof with a downwardly bent portion
52
a
, which has a downward opening
52
b
as a supply outlet matching in position with an upward reception opening
51
a
of an injection sleeve
51
.
Molten magnesium M in the molten metal furnace
55
receives a constant leveling, whereby a “surface level of molten magnesium” (hereinafter called “melt level” or simply “level”) B in the furnace
55
is controlled so that a melt level A in the transfer pipe
52
, which is equivalent to the level B, is maintained near “a height of a bottom point of an inner circumference at a top of tube wall” (hereinafter sometimes called “delivery height” or simply “height”) of the delivery end portion
52
a.
In the above-noted system, molten magnesium M flowing in the pipe
52
is subjected to a flow resistance at both suction and delivery sides of the electromagnetic pump
50
. The flow resistance of pipe
52
is small, but increases with foreign materials sticking on the wall or mixed in metal. In this case, if the coil current of the pump
50
is constant, the pump
50
delivers a reduced amount of molten metal.
To keep the delivery rate free from unfavorable influences of conditions in the transfer pipe
52
, a throttle
53
is installed at a flange joint portion
52
d
of the pipe
52
, and fixed thereto. The throttle
53
provides a sufficient flow resistance for the pump
50
to deliver a corresponding flow rate of molten metal, allowing for the transfer pipe
52
to supply the flow rate of molten metal.
Accordingly, in this molten metal supply system empolying an electromagnetic pump, a metering accuracy of molten metal can be maintained high by exchanging the fixed throttle
53
to another one or cleaning the same.
In order to prevent molten magnesium M from being oxidized, an injection opening
52
c
for injecting anti-oxidization gas G for the molten magnesium M is provided at a top portion of the delivery end portion
52
a
. Anti-oxidization gas G injected from the injection opening
52
c
is filled in a space defined by molten metal of the melt level A and the wall of to the delivery end portion
52
a
of the transfer pipe
52
, so that molten metal M to be supplied to the injection sleeve
51
is prevented from oxidization. The anti-oxidization gas G is also injected in the molten metal furnace
55
, and a space above the melt level B in the furnace
55
is filled with the gas G.
As the anti-oxidization gas G, there is used a diluted antideflagrant gas in which sulfur hexafluoride (hereinafter referred to as “SF
6
”) is diluted with dried air, or an inert gas such as argon.
In
FIG. 1
, reference numeral
54
denotes a heater, reference numeral
57
denotes an injection plunger driven in a reciprocating manner within the injection sleeve
51
by a hydraulic operation mechanism
58
, and reference numeral
59
denotes a metal mold cavity communicating with the injection sleeve
51
.
In the conventional molten metal supply system empolying an electromagnetic pump, however, as the throttle
53
is fixed to the flange joint portion
52
d
of the transfer pipe
52
, there occur needs of pipe disconnection for maintenance services, such as for cleaning to the throttle
53
or pipe wall therearound or for replacement of the throttle
53
. In particular, in the case of molten magnesium (including molten magnesium alloy), the molten metal tends to be oxidized or combusted during such a service.
Though one of SF
6
dilute antideflagrant gas and an inert gas such as argon is generally used as anti-oxidization gas G, such a use of single gas has a potential possibility of causing molten metal oxidization or loose ending or cut of molten metal supply. There is a problem of increased oxidization, followed by difficulty in maintenance work, and a supply amount of molten metal becomes unstable, so that a stable die casting work can not be performed.
That is, SF
6
dilute antideflagrant gas is relatively inexpensive and has a high antideflagrant effect owing to a high dilution rate thereof. However, when molten magnesium M is transferred to the injection sleeve
51
by the electromagnetic pump
50
, oxidization of the molten magnesium M and/or reaction product is easy to occur and the ending of molten magnesium supply at the opening
52
b
of the delivery end portion
52
a
becomes sharp.
An inert gas such as argon is used alone, which becomes relatively expensive, however, oxidization of the molten magnesium M is reduced and the ending of molten magnesium supply is improved. In an ordinary use, however, the antideflagrant nature is relatively inferior, and there is a problem that, when the melt level M in the molten metal furnace
55
varies at an ON/OFF time of the constant melt level control and external air enters in/leaves from the molten metal furnace
55
, the molten magnesium M sticking on an inner surface of the delivery end portion
52
a
is oxidized.
Furthermore, in the conventional molten metal supply system empolying an

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